1. Field of the Invention
The present invention relates generally to metal container bodies of the type having a seamless sidewall and a bottom formed integrally therewith. More particularly, the present invention relates to bottom contours that provide increased dome reversal pressure, that provide greater resistance to damage when dropped, that minimize or prevent growth in the height of a container in which the beverage is subjected to pasteurizing temperatures and/or extreme temperatures encountered in shipping and storage. Further, the present invention relates to apparatus and method for providing these improved bottom contours.
2. Description of the Related Art
There have been numerous container configurations of two-piece containers, that is, containers having a container body with an integral bottom wall at one end, and an open end that is configured to have a closure secured thereto. Container manufacturers package beverages of various types in these containers formed of either steel or aluminum alloys.
In the production of these container bodies, it is important that the body wall and bottom wall of the container be as thin as possible so that the container can be sold at a competitive price. Much work has been done on thinning the body wall.
Aside from seeking thin body wall structures, various bottom wall configurations have been investigated. An early attempt in seeking sufficient strength of the bottom wall was to form the same into a spherical dome configuration. This general configuration is shown in Dunn et al., U.S. Pat. No. 3,760,751, issued Sep. 25, 1973. The bottom wall is thereby provided with an inwardly concave dome or bottom recess portion which includes a large portion of the area of the bottom wall of the container body. This domed configuration provides increased strength and resists deformation of the bottom wall under increased internal pressure of the container with little change in the overall geometry of the bottom wall throughout the pressure range for which the container is designed.
The prior art that teaches domed bottoms also includes P. G. Stephan, U.S. Pat. No. 3,349,956, issued Oct. 31, 1967; Kneusel et al., U.S. Pat. No. 3,693,828, issued Sep. 26, 1972; Dunn et al., U.S. Pat. No. 3,730,383, issued May 1, 1973; Toukmanian, U.S. Pat. No. 3,904,069, issued Sep. 9, 1975; Lyu et al., U.S. Pat. No. 3,942,673, issued Mar. 9, 1976; Miller et al., U.S. Pat. No. 4,294,373, issued Oct. 13, 1981; McMillin, U.S. Pat. No. 4,834,256, issued May 30, 1989; Pulciani et al., U.S. Pat. No. 4,685,582, issued Aug. 11, 1987; and Pulciani, et al., U.S. Pat. No. 4,768,672, issued Sep. 6, 1988.
Patents which teach apparatus for forming container bodies with inwardly domed bottoms and/or which teach container bodies having inwardly domed bottoms, include Maeder et al., U.S. Pat. No 4,289,014, issued Sep. 15, 1981; Gombas, U.S. Pat. No. 4,341,321, issued Jul. 27, 1982; Elert et al., U.S. Pat. No. 4,372,143, issued Feb. 8, 1983; and Pulciani et al., U.S. Pat. No. 4,620,434, issued Nov. 4, 1986.
Of the above-mentioned patents, Lyu et al. teaches an inwardly domed bottom in which the shape of the domed bottom is ellipsoidal.
Stephan, in U.S. Pat. No. 3,349,956, teaches using a reduced diameter annular supporting portion with an inwardly domed bottom disposed intermediate of the reduced diameter annular supporting portion. Stephan also teaches stacking of the reduced diameter annular supporting portion inside the double-seamed top of another container.
Kneusel et al., in U.S. Pat. No. 3,693,828, teach a steel container body having a bottom portion which is frustoconically shaped to provide a reduced diameter annular supporting portion, and having an internally domed bottom that is disposed radially inwardly of the annular supporting portion. Various contours of the bottom are adjusted to provide more uniform coating of the interior bottom surface, including a reduced radius of the domed bottom.
Pulciani et al., in U.S. Pat. Nos. 4,685,582 and 4,768,672, instead of the frustoconical portion of Kneusel et al., teach a transition portion between the cylindrically shaped outer wall of the container body and the reduced diameter annular supporting portion that includes an upper annular arcuate portion that is convex with respect to the outside diameter of the container body and a lower annular arcuate portion that is concave with respect to the outside diameter of the container body.
McMillin, in U.S. Pat. No. 4,834,256, teaches a transitional portion between the cylindrically shaped outer wall of the container body and the reduced diameter annular supporting portion that is contoured to provide stable stacking for containers having a double-seamed top which is generally the same diameter as the cylindrical outer wall, as well as providing stable stacking for containers having double-seamed tops that are smaller than the cylindrical body. In this design, containers with reduced diameter tops stack inside the reduced diameter annular supporting portion; and containers with larger tops stack against this specially contoured transitional portion.
Supik, in U.S. Pat. No. 4,732,292, issued Mar. 22, 1988, teaches making indentations in the bottom of a container body that extend upwardly from the bottom. Various configurations of these indentations are shown. The indentations are said to increase the flexibility of the bottom and thereby prevent cracking of interior coatings when the containers are subjected to internal fluid pressures.
In U.S. Pat. No. 4,885,924, issued Dec. 12, 1989, which was disclosed in W.I.P.O. International Publication No. WO 83/02577 of Aug. 4, 1983, Claydon et al. teach apparatus for rolling the outer surface of the annular supporting portion radially inward, thereby reducing the radii of the annular supporting portion. The annular supporting portion is rolled inwardly to prevent inversion of the dome when the container is subjected to internal fluid pressures.
Various of the prior art patents, including Pulciani et al., U.S. Pat. No. 4,620,434, teach contours which are designed to increase the pressure at which fluid inside the container reverses the dome at the bottom of the container body. This pressure is called the static dome reversal pressure. In this patent, the contour of the transitional portion is given such great emphasis that the radius of the domed panel, though generally specified within a range, is not specified for the preferred embodiment.
However, it has been known that maximum values of static dome reversal pressure are achieved by increasing the curvature of the dome to an optimum value, and that further increases in the dome curvature result in decreases in static dome reversal pressures.
As mentioned earlier, one of the problems is obtaining a maximum dome reversal pressure for a given metal thickness. However, another problem is obtaining resistance to damage when a filled container is dropped onto a hard surface.
Present industry testing for drop resistance is called the cumulative drop height. As performed for tests reported herein, a filled container is dropped onto a steel plate from heights beginning at three inches and increasing by three inches for each successive drop. The drop height resistance is then the sum of all the distances at which the container is dropped, including the height at which the dome is reversed, or partially reversed. That is, the drop height resistance is the cumulative height at which the bottom contour is damaged sufficiently to preclude standing firmly upright on a flat surface.
In U.S. patent application 07/505,618 having common inventorship entity, and being of the same assignee as the present application, it was shown that decreasing the dome radius of the container body increases the cumulative drop height resistance and decreases the dome reversal pressure. Further, it was shown in this prior application that increasing the height of the inner wall increases the dome reversal pressure.
However, as the dome radius is decreased for a given dome height, the inner wall decreases in height. Therefore, for a given dome height, an increase in cumulate drop resistance, as achieved by a decrease in dome radius, results in a decrease in the height of the inner wall together with an attendant decrease in the dome reversal pressure.
Thus, one way to achieve a good combination of cumulative drop height and dome reversal pressure, is to increase the dome height, thereby allowing a reduction in dome radius while leaving an adequate wall height. However, there are limits to which the dome height can be increased while still maintaining standard diameter, height, and volume specifications.
An additional problem in beverage container design and manufacturing has been in maintaining containers within specifications, subsequent to a pasteurizing process, when filled beverage containers are stored at high ambient temperatures, and/or when they are exposed to sunlight.
This increase in height is caused by roll-out of the annular supporting portion as the internal fluid pressure on the domed portion applies a downward force to the circumferential inner wall, and the circumferential inner wall applies a downward force on the annular supporting portion.
An increase in the height of a beverage container causes jamming of the containers in filling and conveying equipment, and unevenness in stacking.
A large quantity of containers are manufactured annually and the producers thereof are always seeking to reduce the amount of metal utilized in making container bodies while still maintaining the same operating characteristics.
Because of the large quantities of container bodies manufactured, a small reduction in metal thickness, even of one ten thousandth of an inch, will result in a substantial reduction in material costs.